Starting this week, Microsoft will feed Windows Vista Ultimate users an update that sniffs out pirated copies, a company manager said Tuesday.

The update, which will hit some Vista Ultimate systems via Windows Update this week, and others in the weeks to come, is the newest move in an anti-activation crack campaign Microsoft launched almost exactly a year ago.

The newest update targets SoftMod, an activation hack that tricks Vista into thinking it's being booted on a PC that had the operating system installed -- and activated -- at the factory. Typically, computer makers pre-activate Windows before they ship systems, eliminating the chore for customers.

SoftMod can be used to created a bootable CD, which then must be used each time the PC is booted, or with care, it can be installed on the machine's hard drive.

According to Alex Kochis, a Microsoft senior product manager in the Windows Genuine Advantage (WGA) group, the SoftMod detection update will be offered only to Vista Ultimate users. "We're releasing this update to Windows Vista Ultimate Edition only at this time and only to systems with English as their primary language," Kochis said in an entry to the WGA blog.

Kochis did not say why Microsoft was sending the update only to Vista Ultimate PCs, although the move may have something to do with that edition's popularity among pirates. Vista Ultimate is the most expensive and most feature-packed version of the operating system and is the dominant edition on file-sharing sites that traffic in illegal software.

Last year, Microsoft delivered two activation crack updates to all Vista users as a preliminary step before it launched Service Pack 1 (SP1). Those updates fingered Grace Timer and OEM BIOS, but only notified the user of their presence and offered up a solution. SP1, which was released to the general public several weeks later, also detected the two cracks. If a hacked copy of Vista was upgraded to SP1, Windows would immediately start spewing on-screen messages that the copy is counterfeit.

After receiving the newest update, copies of Vista Ultimate hacked using SoftMod will pop up a warning that reads, "Windows has found software that circumvents Windows activation and interferes with its normal operation. The presence of such software may indicate that your copy of Windows is counterfeit."

The pop-up also includes a link to instructions on how to remove the crack. People not using SoftMod will not see the pop-up.